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A controversial Mars meteorite is once again in the spotlight as scientists use a new kind of analysis on the rock. The study is reminiscent of initial research, published in 1996, suggesting that tiny iron sulfide and iron oxide grains in the meteorite had biological origins, and that tiny, worm-shaped objects in the rock could be the fossilized remains of Martian microbes.

New analysis of a 13,000-year-old Mars meteorite, retrieved from Antarctica, has rekindled the debate about whether the ancient rock holds signs of past microbial Martian life.

The study is reminiscent of initial research, published in 1996, suggesting that very, very tiny -- nanometer-sized -- iron sulfide and iron oxide grains in the meteorite had biological origins, and that tiny, worm-shaped objects in the rock, known as ALH84001, could be the fossilized remains of Martian microbes. The research was widely panned, and the NASA team making claims for life on Mars subsequently retreated.

Now a team of experts at the NASA Johnson Space Center, including the lead astrobiologist in the 1996 study, David McKay, have looked at the rock again using a new analysis technique, called ion beam milling. They conclude that there is enough evidence to rule out at least one geological process as the one that formed the nanocrystal iron grains. That leaves something that was once living -- biology -- as a possible cause.